The communication system that is a successor to WCDMA and HSDPA i.e. the LTE (Long Term Evolution) has been studied by 3GPP that is the standardization group of WCDMA, and as a radio access scheme, OFDMA (Orthogonal Frequency Division Multiplexing Access) is defined in downlink, while SC-FDMA (Single-Carrier Frequency Division Multiple Access) is defined in uplink (for example, see Non-patent Document 1).
OFDMA is a system for dividing a frequency band into a plurality of narrow frequency bands (subcarriers), and assigning data onto each frequency band to perform transmission, actualizes high-speed transmission and is capable of enhancing spectral efficiency, by densely arranging subcarriers in the frequency domain without interfering with one another even with part thereof overlapping.
SC-FDMA is a transmission system for dividing the frequency band so that a plurality of terminals uses different frequency bands to perform transmission, and thereby enabling interference among the terminals to be reduced. SC-FDMA has the feature that the variation in the transmission power is decreased, and therefore actualizes low power consumption in the terminal and wide coverage.
In LTE, discontinuous reception (DRX) control is applied. The discontinuous reception control is applied in the case that the base station apparatus and the user equipment are connected with each other and that data to communicate does not exit, and the user equipment in the discontinuous reception state receives the Physical Downlink Control Channel (PDCCH) at some intervals i.e. intermittently. In this case, it is essential only that the user equipment receives the PDCCH intermittently instead of all the timing, and it is thereby possible to reduce power consumption in the battery (butter saving). The time duration to intermittently receive the Physical Downlink Control Channel (PDCCH) in the above-mentioned discontinuous reception control is referred to as ON duration of DRX or On-duration. Further, a cycle to On-duration is referred to as the DRX cycle.
In mobile communications, radio link states in uplink and downlink are monitored, and when the radio link state in uplink or downlink deteriorates, to recover the deteriorated radio link state, the radio base station or mobile station UE performs the processing for reestablishing the connection state. For example, the radio base station monitors the radio link quality of uplink signals transmitted from the mobile station, and when the radio link quality deteriorates, is capable of instructing the mobile station to reestablish uplink timing synchronization, or to reestablish the radio link state.